Effect of different sized transverse square grooves on a turbulent boundary layer

The effect of three different sized transverse square grooves (5, 10, and 20 mm) on a turbulent boundary layer was investigated at two values of momentum thickness Reynolds numbers (Rθ=1,000 and 3,000) using hot-wire anemometry. The ratios of the groove depth to the boundary layer thickness (d/δ0) are approximately 0.07, 0.13, and 0.27. Wall shear stress (τw), mean velocity (U), and turbulence intensity downstream of the grooves are compared to those on a corresponding smooth wall The effects of the grooves are more significant at the higher Rθ, with the most pronounced effects caused by the largest size groove. There is an increase in mean velocity (U), streamwise (u′/U0), and wall-normal (ν′/U0) turbulence intensities in the near-wall region immediately downstream of the grooves. The increase propagates outwards in the layer as the streamwise distance increases downstream of the grooves. The increase in ν′/U0 is much more significant than that of u′/U0, which is also evident in the spectra of u′ and ν′. There is an increase in τw over the smooth wall value immediately downstream of the grooves at Rθ=1,000, with the increase being more pronounced as the groove size increases. The growth of the internal layer downstream of the grooves is found to scale with the groove size, and is more rapid at Rθ=3,000.